The present invention relates to electrical equipment, and particularly concerns apparatus and methods for the effective grounding or earthing of electrical equipment while the equipment is isolated from a mains supply during repair or maintenance.
Electrical installations such as computers, network servers and the like are conventionally supplied with electricity from a mains supply. The connection to the mains supply comprises a live and a neutral connection supplying the electrical power, and a ground or earth connection which is connected to the chassis of the equipment. The electrical connectors of the mains supply are in the form of female sockets having recesses to accept the projections of a male plug associated with the equipment. The male plug may be at one end of a cord whose other end is permanently connected to the equipment. Alternatively, the male plug may be a so-called xe2x80x9cac inletxe2x80x9d fixedly mounted to the equipment, and the connection between the plug of the equipment and the socket of the mains supply may be made by means of a cord having a cord plug at one end and a cord socket at the other, the cord plug being compatible with the mains socket, and the cord socket being compatible with the plug or xe2x80x9cac inletxe2x80x9d of the equipment.
When repair or maintenance is to be carried out on an electrical apparatus, it is conventional to ensure the safety of the operative by disconnecting the apparatus from the mains supply, either by disconnecting the plug from the mains socket, or by removing the cord socket from the plug of the apparatus. This not only isolates the equipment from the mains voltage, but also removes the ground or earth connection to the chassis of the equipment.
The repair of semiconductor circuits however requires the operative to be able to access a secure ground connection, in order to avoid the accumulation of electrostatic charges which may damage sensitive semiconductor devices. Conventionally a connection point is provided on the apparatus chassis for the service operative to connect one end of an earthing strap, the other end of which is attached to the operative. The connection point may be a conductive button or socket fixed to the chassis, or may be a bare metal area of the chassis to which the strap is attached by a crocodile clip or the like. However, there is no standard position for such a connection point on the chassis of electrical apparatus, and the operative often has to spend time to locate the connection point. Furthermore, when the power cord is disconnected from the apparatus, the earth connection to the chassis is severed, and even if the service operative is connected to the chassis by an earth strap, neither may be reliably earthed.
The repair operative is therefore faced with the choice of disconnecting the mains cable and losing the secure ground connection, or leaving the equipment connected to the mains to ensure a ground connection, but risking exposure to internal components of the equipment at mains voltages.
A need therefore exists for a device which can effectively isolate an electrical apparatus from the mains voltage, while maintaining the ground or earth connection to the apparatus.
One embodiment of the present invention provides an adaptor device connectable between a plug of an electrical apparatus having live, neutral and earth (ground) connectors and a mains supply socket having live, neutral and earth (ground) connectors, the adaptor device having a first interface compatible with the mains supply socket and having an earth contact electrically connectable to the earth connector of the mains supply, and a second interface compatible with the plug and having an earth contact electrically connectable to the earth connector of the plug, the adaptor device further comprising an electrical conductor connecting only the earth contacts of the first and second interfaces, and maintaining live and neutral connectors of the mains supply isolated from the equipment.
The adaptor may be in the form of an elongate component having the first and second interfaces at first and second ends of the component. Alternatively, the adaptor may comprise a plug compatible with a mains socket and a socket compatible with the plug of the equipment, connected together by a cord providing electrical connection only between earth contacts of the plug and socket, respectively.
The adapter may be further provided with third and fourth interfaces respectively configured to be compatible with a mains supply and a plug of different configurations from those compatible with the first and second interfaces.
The adaptor of the invention enables the operative and the apparatus to be reliably earthed, while isolating the apparatus from the mains voltage.
In a particular embodiment, the adapter may be provided with a stud, socket and/or clip electrically connected to the earth contacts of the adapter, for attaching one end of an earthing strap to the adaptor. The operative can then easily locate the attachment point for the earthing strap, and time spent searching for the attachment point can be saved.
In a further particular embodiment, an earthing strap may be provided at one end with a band, clip or other formation to attach to a service operative, and at the other end with an adapter as described above.
In a yet further embodiment of the adapter, the interface compatible with the apparatus plug may include recesses to receive the live and neutral contacts, respectively, of the apparatus plug, and an electrical conductor to connect the recesses together, so that when the adapter is applied to the apparatus, the live and neutral pins of the apparatus plug are electrically connected together.
In a yet further embodiment of the adapter, the interface compatible with the apparatus plug may include recesses to receive the live and neutral contacts, respectively, of the apparatus plug, and an electrical conductor to connect the sockets together and to the earth connection, so that when the adapter is applied to the apparatus, the live and neutral pins of the apparatus plug are electrically connected together and to earth.
In a further embodiment of the invention there is provided a mains cord for an electrical apparatus having a power inlet, the mains cord having at one end a first interface compatible with an electricity supply socket and at its other end a second interface compatible wiht the power inlet of the apparatus and electrical conductors to connect respectively live, neutral and earth contacts of the first and second interfaces together, the mains cord being further provided with a third interface compatible with either the electricity supply outlet or with the power inlet wherein only an earth contact of the third interface is electrically connected to the earth contacts of the first and second interfaces, and live and neutral contacts of the third interface are electrically isolated from the live and neutral contacts of the first and second interfaces. In a particular development of this embodiment, the live and neutral contacts of the third interface may be electrically connected together and/or to the earth contact. The third interface may be at the one end of the cord, and take the form of a conventional mains plug, or alternatively the third interface may be at the other end of the mains cord and take the form of a cord socket.
A further aspect of the invention concerns an enclosure for electronic circuitry which includes a mains inlet having contacts to engage live, earth and neutral contacts in a connector of a power cord, the mains inlet being so configured that the power cord connector (cord socked) may be engaged therewith in a first configuration in which contact is made with all three of the live, neutral and earth contacts of the connector, and in a second configuration wherein contact is made only with the earth conntact. In a first embodiment of this aspect, the mains inlet is provided with two plug formations engageable with the mains connector lead, one of the plug formations having three contacts and the other plug formation having a single contact to engage the earth contact of the connection cord. In a second embodiment of this aspect, the mains inlet has three electrical contacts, and is so configured that the connection cord may be engaged in a first orientation wherein connection is made with the earth, live and neutral contacts, and in a second orientation wherein connection is only made with the earth contact of the mains inlet.
The invention further provides a method of servicing or repairing a mains-powered electrical apparatus using the adapter and/or earth strap as described above.